One fundamental problem residing in a WPCN is the well-known “doubly-near-far” phenomenon [1]} where a device that is far away from the HAP harvests less energy in the DL WPT but consumes more to transmit information in the UL WIT than that of a device nearer to the HAP. As a result, the throughput of a far device may only have significantly lower throughput than a nearby device, leading to a severe user unfair issue in WPCNs. Fortunately, it can be well alleviated by properly deploying the IRS. To illustrate this, we show in Fig. REF  the sum throughput and devices' throughput versus the IRS's horizontal location, i.e., (\(x\) , 0, 0) m, by considering a WPCN with two devices, namely D1 and D2, who are located in (7, 0, 0) m and (10, 0, 0) m, respectively. It is observed from Fig. REF  that without IRS, the throughput of D1 outperforms that of D2 significantly as expected, whereas by deploying the IRS around the far device (D2), the throughputs of the two devices can be well compromised and both of them are much higher that those in the case without IRS. This is because the IRS is able to effectively compensate more path loss for the device far from the HAP as compared to the nearby device, which helps resolve the user unfairness issue incurred by “doubly-near-far” phenomenon.
